Circuit boards and other modules are often assembled with pick-and-place machines containing multiple tape feeders each having components mounted to component carrier tapes wound around a reel. The component carrier tape unwinds as the pick-and-place machine uses components and empties the tape. New tapes may be spliced onto the tape before it is emptied. This avoids removing the feeder from the machine to load a new reel of components to the feeder that is running out of components.
This splicing operation suffers from the problem that a wrong reel (i.e., a reel with a wrong part number) can easily be spliced onto the existing reel. Often, bar code scanning of the new reel part number will prevent mistakes, but there is no guarantee that the machine operator will follow the instructions and correctly scan every new component reel when splicing.
One solution is to detect a splice with a splicing sensor. The component carrier tape is typically spliced with a small metallic strip, such as a copper strip, to reinforce the tape so that it will not jam in the feeder. Some existing systems include intelligent feeders which have an inductive sensor at the front of the feeder and wiring connecting the sensor to the machine. The inductive sensors detect the metallic strip and alert the machine of the component carrier tape splice. Metallic strips can also be detected using electrodes positioned on the feeder. As the metallic strip slides pass the electrodes, the metal strip comes into contact with the electrodes creating a closed loop circuit to indicate the presence of a splice. Other systems have an optical sensor attached to the feeder and positioned at the sprocket hole position of the component carrier tape. The sensor is adapted to measure the transmission of light through the sprocket holes of the component carrier tape. The splice is created using an adhesive splicing tape such that the width of the tape used on top side of the component carrier tape is wider than the splicing tape on the bottom side of the component carrier tape. The wider adhesive tape covers the sprocket holes in the component carrier tape and prevents the transmission of light through the holes. The regular width adhesive tape on the bottom of the component carrier tape leaves the sprocket holes exposed allowing the component carrier tape to be advanced by the sprocket on the feeder. The adhesive tape used on the top side of the component carrier tape is sufficiently thick so as not to allow any light to pass through the sprocket hole. Thus, a splice is detected when the optical sensor fails to detect the expected light signal through the sprocket hole.
Intelligent feeders are widely available and are typically more expensive than their ‘non-intelligent’ counterparts. Retrofitting an existing ‘non-intelligent’ system with an inductive sensor system can be difficult due to the extensive modifications that are typically required, and very costly. For example, a 100-feeder-slot machine will typically have about 200 feeders to support the piece of equipment.
An alternative solution is found in my U.S. Pat. No. 6,817,216, the entire contents of which are hereby incorporated by reference for all purposes. The system in U.S. Pat. No. 6,817,216 includes an example employing a color sensitive optical sensor disposed on the machine's pickup head. In this case, the optical sensor is used to detect a color associated with the splice connection. This scheme avoids the need for intelligent feeders or modifications to multiple feeders, and only requires modification to the machine pickup head. However, because the pickup head frequently moves at high speeds, operators and pick-and-place machine providers prefer to avoid this type of modification as it will affect the operating dynamic of the pickup head.
What is needed, therefore, are better splicing and splice detection methods that allow for un-interrupted operation of pick-and-place machines while providing reliable operation. Also needed are systems that allow retrofitting of pick-and-place machines and their control systems to have splice detection capability, without extensive modifications to the tape feeders or the machines.